Paleomagnetism and geobarometry of the Big Creek Batholith suggests that the Yukon-Tanana Terrane has been a parautochthon since Early Jurassic

The similar to 190+/-5 Ma Big Creek hornblende-syenite and monzogabbro bath olith has an outcrop area of similar to 400 km(2) within the Yukon-Tanana T errane (YTT) in the west-central part of the Yukon Territory of Canada. Pal eomagnetic analysis of 245 specimens from 21 sites isolates a characteristi c remanent magnetization residing principally in magnetite and subordinatel y in hematite. The unit mean direction for the batholith from 16 normal pol arity and two reverse polarity sites is D = 305.6 degrees, I = 72.1 degrees (alpha (95) = 3.9 degrees). Al-in-hornblende geothermobarometry at six loc ations yields emplacement depths of similar to 16+/-2 km. Three arguments s uggest that the characteristic remanent magnetization was acquired on exhum ation at similar to 180 Ma. More significantly, the pole position indicates no northward translation but counterclockwise rotation, implying that the YTT formed close to its present position on the Jurassic margin of the Nort h American craton, This implies, in turn, that the allochthonous terranes o f the Intermontane and Coast belts of the western Cordillera impacted onto, and overrode, the YTT upon accretion during Late Cretaceous to Middle Eoce ne time. (C) 2000 Elsevier Science B.V. All rights reserved.